Various kinds of piezoelectric resonator are known.
In a conventional first example, a resonator crystal is constituted by a bi-planar, planar-convex, or bi-convex quartz slab of circular outline, with metal electrodes referred to as "adherent" electrodes deposited directly on the main faces thereof.
In another embodiment, the quartz slab with adherent electrodes is externally delimited by a ring of quartz serving as a support for the resonator crystal.
In yet another embodiment, the resonator crystal is connected to a ring of quartz via bridges cut-out in a solid crystal. The electrodes may be adherent or non-adherent. When non-adherent, the electrodes are deposited on quartz slabs having the same cut as the crystal and a similar shape, and only the rings of the electrode-supporting slabs come into contact with the ring of the vibrating crystal.
In this disposition where the crystal is self-suspended without any metal diffusion, thermal compression, or fixing means associated with the active portion of the crystal, it is possible to obtain excellent frequency stability and also better resistance to shock.
However, such frequency stability requires accurate temperature control and the slightest fluctuation in temperature has an effect on the frequency of oscillation of the resonator crystal. That is why it is usual for the resonator to be placed in a very high accuracy thermostat for limiting such fluctuations, but which unfortunately consumes a non-negligible amount of power.